In the technology of injector systems for the injection of high pressure fuel into the combustion areas of direct-injection combustion engines, injector systems with high pressure collecting areas are employed. Pressure pulsations in the fuel can be dampened by means of the fuel volumes contained in the high pressure collecting area (Common Rail), and a uniformly high pressure level can be guaranteed for all of the injectors of the injection system. The start of injection and the amounts injected are adjusted by means of the electrically controllable injectors, which can be introduced at the cylinder heads of direct-injection combustion engines without substantial alterations.
EP 0 657 642 A2 discloses a fuel injection apparatus for fuel engines. These involve a high pressure collecting area fillable by a high pressure fuel pump, from which lead out high pressure conduits to the individual injection valves. Therewith are employed in the individual high pressure conduits, control valves for the control of the high pressure injection in the injection valves, as well as an additional reservoir area between these control valves and the high pressure collecting area. In order to avoid too high a system pressure being continuously fitted to the injection valves, the control valves are so executed that during the injection pauses at the injection valves, their connection to the reservoir area is locked and a connection between the injection valves and a relief area is set up.
DE 197 01 879 A1 also refers to a fuel injection apparatus for combustion engines. The solution from the state of the art disclosed by this reference is also the provision of a relief canal, which can be connected with a workspace hydraulically controllable by means of the control valve links, in order to thereby attain an adjustment of the timing position of the control valve links.
However, the need still exists as before to bring about a further decrease in both contaminant emissions and noise pollution from direct-injection combustion engines. Such advancements can be essentially complied with by means of an improved injector functioning. If a more simple construction of a pressure-controlled injector can be realized, then mastery of the production process for such injectors can be significantly increased so as to provide a higher degree of standardization during the production of the injectors. This would considerably influence the manufacturing costs of such injector systems.
With prevailing pressures of clearly more than 1400 bar within the fuel injection systems for direct-injection combustion engines, a further increase in the system pressure is obtainable only with difficulty. The pump conduits necessary for this inevitably lead to an increase in the dissipation losses that occur by means of the introduction of heat into the fuel. However, this is highly undesirable. On the other hand, the previously known injectors that have been utilized are constructed properly complex and require, for example, a drainage throttle and an input throttle, control pistons, sometimes a doubled pin guide and that sort of thing. In order to realize the desired construction characteristics in prepared injectors in a cost-favorable manner, expensive preparation steps are necessary which unfavorably influence the total manufacturing costs of such injectors.
The necessary activation of drainage and input throttles, with consideration of the injection tolerances, impairs the opening and closing behavior of today""s injector constructions especially for the employment of high pressure collecting areas (Common Rail).
With both suggested variations in accordance with the present invention, either with or without utilization of the uniform pressure transmission unit, one obtains on the one hand a standardized cost-favorable preparation of injectors, taking into account the principles of construction economics. In addition to the elevation of pressure, one can further take advantage of the fuel volumes involved in the fuel injection. The increase in pressure, however, is only provided during the injection phase, so that leakages based upon irregularities in fuel viscosity and the overflow effects resulting therefrom, are not critical. In order to avoid an over-stressed injection rate during the ignition delay, occuring on account of the increase in pressure of the fuel injection, a throttle element for dampening of the injection rate can be positioned before the injector entrance. An excessive injection rate would clearly be the factor responsible for an elevation in noise level, as well as a rise in the amounts of NOx-emissions.
In addition to the increase in pressure effective only during the injection window, and the thereby improved safety of the injector with regard to the behavior of viscosity irregularities within the injector system, a greater opening and closing dynamic (rapid spill) can be attained by means of a 2/2-way valve close to the nozzle, which was previously not obtainable in these devices using throttle elements. Moreover, the injection interval between the preliminary injection phase and the subsequent main injection phase are considerably shortened, by means of the 2/2-way valve close to the nozzle, since shorter running times can then be obtained within the conduit system.
In order to be able to maintain a higher standard pressure within the fuel injection system, indeed depending upon the type of use, one need simply to integrate a pressure retaining valve, for example a uniform pressure valve.
The novel features which are considered as characteristic for the present invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.